The present invention relates to a semiconductor device, and more particularly to a semiconductor device whose wiring structure is formed by a multilayer structure.
In conjunction with trends toward higher integration and higher speed of semiconductor devices in recent years, the copper (Cu) wiring having a lower electrical resistance than the conventional aluminum (Al) wiring has come to be introduced. However, if copper (Cu) atoms are diffused and enter a silicon (Si) substrate or an insulating film, there is a possibility of deteriorating the device characteristics, so that an adjacent conductive film (first conductive film) for preventing the diffusion of the copper (Cu) atoms is formed adjacent to a copper (Cu) film. As materials of this adjacent conductive film, high-melting-point metals such as titanium nitride (TiN), tungsten (W), and tantalum (Ta) have been studied, as described in Nikkei Microdevices (June 1992 issue, pp. 74-77). However, if these materials are used as the adjacent conductive film, their adhesion to the plated film of copper (Cu) used for wiring is weak, so that rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) have been proposed in Japanese Patent Application Laid-Open Hei 10-229084 (JP-A-10-229084) as materials of the adjacent conductive film for improving the adhesion.
In the manufacture of semiconductor devices which are finely patterned for higher integration, since there are cases where chemical mechanical polishing (CMP) is employed as a technique for effecting planarization, it is important to improve adhesion between the respective films formed. However, if rhodium (Rh), ruthenium (Ru), iridium (Ir), or osmium (Os) is used as the material of the adjacent conductive film in the copper (Cu) wiring, the adhesion between copper (Cu) and the adjacent conductive film improves, but there is a problem in that the adhesion between the adjacent conductive film and the insulating film is weak. Further, rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) are liable to produce high stress during film formation, possibly causing defects such as cracks to occur in an adjacent film. Furthermore, with the semiconductor devices which are finely patterned for higher integration, the wiring width becomes narrow, so that there is a problem in that voids and disconnections due to migration are likely to occur.
A first object of the invention is to provide a highly reliable semiconductor device. A second object of the invention is to provide a semiconductor device having a wiring structure whose yield is high. A third object of the invention is to provide a semiconductor device having a multilayer structure in which adhesive fracture is difficult to occur by the use of highly adhesive adjacent conductive film materials for both a main conductive film forming the wiring and an insulating film. Further, a fourth object of the invention is to provide a semiconductor device having a multilayer structure in which defects such as cracks are difficult to occur. Furthermore, a fifth object of the invention is to provide a semiconductor device in which voids and disconnections due to migration are difficult to occur.
The present inventors conducted research strenuously to overcome the above-described problems, and discovered that in a case where a first conductive film for diffusion prevention whose main constituent elements are titanium nitride (TiN), tungsten (W), and tantalum (Ta) is used adjacent to a second conductive film whose main constituent element is copper (Cu), since the lengths of sides of the unit crystal cells of the first conductive film and copper (Cu) substantially differ, the atomic arrangement becomes disarrayed at the interface between the first conductive film and the second conductive film, and the diffusion of the copper (Cu) atoms becomes active, so that adhesive fracture is liable to occur. The present inventors discovered that, to prevent the adhesive fracture at the interface between the copper (Cu) film and the first conductive film, it suffices to suppress the diffusion of the copper (Cu) atoms by using as the first conductive film material a material whose length of the side of the unit crystal cell (lattice constant) is close to that of copper (Cu), i.e., a material in which the difference in the lattice constant (lattice mismatching) with copper (Cu) is small, and that in a case where the melting point of the first conductive film is low, the diffusion of the element constituting the first conductive film becomes active, and the diffusion of the copper (Cu) atoms is accelerated, so that a material having a high melting point is suitable. Further, the present inventors clarified that it is effective in the improvement of adhesion to copper (Cu) to use as the diffusion-preventing adjacent conductive film a material whose lattice mismatching with copper (Cu) is small and which has a melting point not less than 1.4 times that of copper (Cu). More specifically, the present inventors clarified that in a multilayer wiring structure comprising a first conductive film and a second conductive film formed in contact with the first conductive film, the diffusion at the main conductive film is suppressed and the adhesion between the first conductive film and the second conductive film improves in a case where the difference {|apxe2x88x92an|/ap}xc3x97100=A(%) between a short side an in a unit rectangular cell of a closest packed crystal plane formed by the main constituent element of the first conductive film and a short side ap in a unit rectangular cell of a closest packed crystal plane formed by the main constituent element of the second conductive film and the difference {|bpxe2x88x92bn|/bp}xc3x97100=B(%) between a long side bn in the unit rectangular cell of the closest packed crystal plane formed by the main constituent element of the first conductive film and a long side bp in the unit rectangular cell of the closest packed crystal plane formed by the main constituent element of the second conductive film satisfy an inequality {A+Bxc3x97(ap/bp)} less than 13%, and the melting point of the main constituent element of the first conductive film is not less than 1.4 times that of the main constituent element of the second conductive film. Here, the definitions of the short side a and the long side b of a unit rectangular cell forming the crystal plane where the atomic density is the largest, i.e., the closest packed crystal plane, in a bulk crystal are shown in FIG. 2, and a and b are referred to herein as lattice constants. The short side a is the closest interatomic distance in a bulk crystal, and is described on page 28 of xe2x80x9cIntroduction to Solid Physics,xe2x80x9d 1st Vol., 5th Edition (Charles Kittel). In a crystal having a face-centered cubic structure or a closest packed hexagonal structure, the long side b is about 1.73 times the short side a, and in the case of a crystal having a body-centered cubic structure the long side b is about 1.41 times the short side a. Here, the difference A in the short side a and the difference B in the long side b will be referred to as lattice mismatching. Here, the main constituent element of the film means an element which is contained most in the film. Further, kelvin (K) is used as the unit of temperature.
The present inventors clarified that in a case where the first conductive film formed of rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os), and platinum (Pt) whose lattice mismatching A and B with copper (Cu) are small enough to satisfy the aforementioned inequality {A+Bxc3x97(ap/bp)} less than 13% and which have melting points not less than 1.4 times that of copper (Cu) is used as the adjacent conductive film for the copper (Cu) wiring, the adhesion between the first conductive film and the copper (Cu) film improves; however, rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os), and platinum (Pt) have weak bonds with silicon (Si), and since an insulating film containing silicon (Si) is generally amorphous, a strong bond cannot be obtained between the first conductive film and the insulating film containing silicon (Si), so that adhesive fracture is liable to occur. Accordingly, in order to improve the adhesion between the first conductive film and the insulating film while strongly maintaining the adhesion between the first conductive film and the copper (Cu) film, it suffices if an added element which is strongly bonded to silicon (Si) and does not disarray the atomic arrangement of the first conductive film is contained in the first conductive film whose main constituent elements are rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os), and platinum (Pt). The present inventors clarified that the adhesivity between the first conductive film and the insulating film improves in a case where the bond energy between this added element and silicon (Si) is not less than 1.9 times that of the main constituent element of the first conductive film and silicon (Si). Nevertheless, if the difference between the atomic radius of the added element and the atomic radius of the main constituent element such as rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os), and platinum (Pt) becomes not less than 10%, the atomic arrangement o the first conductive film becomes disarrayed, so that the adhesion between the first conductive film and the copper (Cu) film becomes weak. Accordingly, an added element becomes effective in which the difference between the atomic radius of the added element and the atomic radius of the main constituent element of the first conductive film is not more than 10%, and whose bond energy with silicon (Si) is not less than 1.9 times the bond energy between the main constituent element of the first conductive film and silicon (Si). It was clarified that palladium (Pd), cobalt (Co), nickel (Ni), and titanium (Ti) are effective as added elements which satisfy these conditions. Further, it was clarified that the inclusion of such added elements is effective in reducing the internal stress in the first conductive film.
Furthermore, the present inventors clarified that in a case where rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os), and platinum (Pt) whose lattice mismatching A and B with copper (Cu) are small enough to satisfy the aforementioned inequality {A+Bxc3x97(ap/bp)} less than 13% and which have melting points not less than 1.4 times that of copper (Cu) are used as the main constituent elements of the conductive film adjacent to the copper (Cu) film, the diffusion of the copper (Cu) atoms is suppressed, and migration resistance improves.
Namely, to overcome the problems of the invention of this application, the present inventors discovered that it is important to provide a semiconductor device having a multilayer structure comprising on a principle plane side of a semiconductor substrate an insulating film including silicon (Si), a first conductive film formed in contact with the insulating film, and a second conductive film formed in contact with the first conductive film, wherein a difference {|apxe2x88x92an|/ap}xc3x97100=A(%) between a short side an in a unit rectangular cell of a closest packed crystal plane formed by the main constituent element of the first conductive film and a short side ap in a unit rectangular cell of a closest packed crystal plane formed by the main constituent element of the second conductive film and a difference {|bpxe2x88x92bn|/bp}xc3x97100=B(%) between a long side bn in the unit rectangular cell of the closest packed crystal plane formed by the main constituent element of the first conductive film and a long side bp in the unit rectangular cell of the closest packed crystal plane formed by the main constituent element of the second conductive film satisfy an inequality {A+Bxc3x97(ap/bp)} less than 13%, a melting point of the main constituent element of the first conductive film is not less than 1.4 times that of the main constituent element of the second conductive film, the first conductive film contains as an added element at least one different kind of element in addition to the main constituent element, a difference between an atomic radius of at least one kind of added element among the different kinds of elements and an atomic radius of the main constituent element of the first conductive film is not more than 10%, and a bond energy between the added element and silicon (Si) is not less than 1.9 times that of the main constituent element of the first conductive film and silicon (Si).